Gene evolution. Genes encoding members of a kappa chain subgroup have been cloned from recombinant DNA libraries generated in six different wild mouse species. Sequence analysis of these genes is currently in progress. Results from these studies will permit an assessment of multigene evolution during modern speciation and provide insights into mutational mechanisms operating on such families. Growth and regulation. A factor required for plasmacytoma growth in vitro has been purified to apparent homogeneity. Experiments are currently in progress to obtain amino terminal sequence data which will be used to generate a synthetic oligonucleotide probe for gene cloning. Attempts are also underway to raise monoclonal antibodies to this factor. Antibody diversity. Light chains from antibodies to Beta(1,6)-galactan are unusual in that they express an I1e at the point of VK-JK recombination. This amino acid cannot be generated by sequences usually found at the 3' end of VK genes or 5' to JK genes. To determine whether nucleotides generating this amino acid were germ encoded or added during recombination, the germline gene and cDNA encoding this variable region were cloned and sequenced. Results of these studies confirm that the codon for the unusual I1e is in the germline immediately 3' to the normal termination of the VK coding sequence.